The present invention relates to disk drives and, in particular, to disk drives that employ multi-stage actuators to position heads over disk surfaces.
A disk drive is a device that is commonly employed in computer systems to store data. Typically, a disk drive includes: (1) one or more disks that each have a plurality of concentric tracks on which data is stored; (2) a spin motor for rotating the disk or disks; (3) one or more heads that are each capable of writing and/or reading data to/from a track on a disk; (4) an actuator for moving the head or heads to a desired location adjacent to a disk so that data can be written to the disk or read from the disk; and (5) circuitry for transferring data between a disk and a portion of a host computer system that is exterior to the disk drive, such as a random access memory (RAM).
A disk drive also typically includes a servo system that operates to move a head over a defined track on a disk surface and maintain the head over the defined track until directed to move the head over a different track. The servo system maintains the position of the head over a defined track based upon information that is read from a servo track. In one type of drive, the servo tracks are embedded in or coincident with the user data tracks, i.e., the servo track and the user data track form a single physical track with the servo data interspersed among the user data. Typically, the servo track: (1) identifies the particular track over which a head is positioned; and (2) provides data from which the position of the head relative to the center line of the track can be determined. The identification of the particular track is primarily used when the head is being moved from one track to another track (which is commonly known as a seek operation) to determine when the head is positioned over the desired track. Once the head is over the desired track, data indicating the position of the head relative to the center line of the track is determined and used to maintain the head over the desired track (which is commonly known as a tracking operation). For example, if the data indicates that the head is positioned to one side of the center line, the servo system causes the actuator to move the head towards the center line.
As track densities increase, it becomes increasingly difficult for the servo system to maintain the head over a desired location on the disk surface. This difficulty stems, in part, from the difficulty that the servo system has in making the very fine adjustments needed to position the heads over increasingly narrow tracks with an actuator that has relatively high inertia and multiple mechanical resonant modes. To address this problem, a two-stage (or dual-stage) actuator has been implemented that includes a primary actuator and a secondary actuator. The primary actuator is used by the servo system to perform large or coarse movements of the head. The secondary actuator, which rides on the primary actuator, is used by the servo system to perform the small or fine movements of the head needed to maintain the head over the increasingly narrower and denser tracks. The primary actuator simultaneously adjusts the position of all the heads in the disk drive, whereas the secondary actuators each adjust the position of a single head without affecting the position of the other heads.
The throughput or data transfer rate of a disk drive is a key performance characteristic. Needless to say, there is a continuing need to increase the speed at which the disk drive can transfer data to and from the exterior environment.
The present invention is directed to disk drive that uses a multi-stage actuator to achieve an increased throughput or data transfer rate between the disk and the exterior environment.
A disk drive is provided that includes a disk that is capable of storing data on both surfaces of the disk. Associated with each surface of the disk is a head for transferring data between the disk surface and the exterior environment. A multi-stage actuator is used to move the heads to desired positions over the disk surfaces for the transfer of data. The multi-stage actuator includes a primary actuator for coarsely positioning the heads and secondary actuators (one per head) that position the heads more finely than the primary actuator is readily capable of doing. A data transfer device uses the primary and secondary actuators in a manner that provides an increased throughput (i.e., increased rate of data transfer per unit time), particularly with respect to the transfer of large data files. The data transfer device makes use of both heads to transfer the data associated with a particular file between the disk and the exterior environment.
Typically, the secondary actuators provide a range of motion that permits the heads to be positioned over a number of tracks when the primary actuator is at an established position. Consequently, the data transfer device can realize even greater throughput by causing the secondary actuators to move the heads to write and read to and from a number of different tracks while gradually repositioning the primary actuator so that the coarse positioning operation need not interrupt the data transfer operation.
In one embodiment, the data transfer device simultaneously uses both heads to transfer data between the disk and the exterior environment. In this embodiment, the data transfer device, in the case of a write operation, divides a file into segments. The odd numbered segments are to be written to a first disk surface using the first head, and the even numbered segments are to be written to a second disk surface using the second head. The data transfer device also causes the primary actuator to coarsely position the heads and the secondary actuators to finely position the heads. Once the heads are positioned, the data transfer device causes the odd numbered segments to be provided to the first head at the same time that the even numbered segments are being provided to the second head. Consequently, the throughput is substantially doubled relative to a disk drive that only uses one head at a time to write data to a single disk surface. Similarly, during a read operation, the data transfer device positions the first and second heads, the first head reads the odd numbered segments from the first disk surface at the same time that the second head reads the even numbered segments from the second disk surface, the segments are combined into the file and the file is transferred to the exterior environment.
In another embodiment, the data transfer device uses each head in an alternating fashion to transfer data between the disk and the exterior environment such that, after a portion of a file is transferred by one of the heads, one head is transferring data while the other head is being moved by a secondary actuator to a new location over the disk to perform the next data transfer. For example, in the case of a write operation, the data transfer device initially causes the primary actuator to coarsely position the heads and the secondary actuators to finely position the heads over the tracks where the first segments of a particular file are to be written. The data transfer device then causes the first head to write data on the first disk surface, and after the first head has finished writing, causes the second head to write data to the second disk surface. Further, while the second head is writing data to the second disk surface, the data transfer device uses the secondary actuator associated with the first head to reposition the first head over the next track on which data is to be written. By the time the second head is finished writing data to the second disk surface, the first head is positioned over the desired track on the first disk surface and begins writing to the first disk surface. This process of writing one portion of a file with one head while repositioning the other head for subsequently writing the next portion of the file continues until the entire file has been written. Similarly, during a read operation, the data transfer device alternatingly uses the heads to read the data file, and while one head is reading the data the other head is positioned over the desired track where the next read operation occurs.